The RSS level is a measure of the signal strength, present at the antenna, of an RF useful signal. All the radiotelephones, for example portable ones, have a defined range for the RF useful signal, in which they can operate with a tolerable error. The boundaries of this range are defined by specific RSS values. In order for the radiotelephone to be able to determine whether the received RF useful signal is still inside this range, the signal level thereof must be measured. If the measured signal strength is outside the defined range, the telephone automatically changes the channel and/or he base station.
A limiter circuit is used in conventional receiver structures in order to establish these boundaries. This permits a simple and cost-effective design in the receive path of the radiotelephone. A substantial disadvantage of the use of a limiter circuit is its narrow dynamic range. A typical range of the signal strength which can be measured directly using a limiter circuit is, for example, -100 dBm to -25 dBm.
If the radiotelephone has to operate near a base station, it is frequently necessary to raise the upper boundary of the RSSI range, for example to -10 dBm. However, this RSS value can no longer be measured directly by the limiter circuit. It is therefore customary to use a separate measuring device at a point in the receive path at which the signal has a lower level, or a known and separate attenuator is connected upstream of the limiter circuit. Such a connection can be performed, for example, via a PIN diode.
As a result of such a separate measurement of the signal level or as a result of the connection of a known and separate attenuator, however, the circuit arrangement becomes more complicated, the radiotelephone becomes more susceptible to error, and the design becomes more expensive.